Dibutyryl cyclic AMP decreases capacitation time in vitro in mouse spermatozoa

Epididymal mouse sperm suspensions were preincubated for various times in medium containing glucose and/or dibutyryl cyclic AMP and then assessed for fertilizing ability in vitro, loss of the acrosome and motility changes. Capacitation time was significantly reduced by exposure to glucose and 0.1 mM-dbcAMP for 30 min as evidenced by early and synchronous fertilization of eggs, compared with glucose alone. Although this was accompanied by a precocious development of whiplash motility, the rate of acrosome loss in isolated sperm suspensions was not accelerated by the presence of exogenous cyclic nucleotide. Exposure of spermatozoa to 1 mM-dbcAMP in the presence of glucose resulted in very poor fertilization, but the effect could be prevented by withholding glucose until eggs were introduced; this may be due to free butyrate in the system since the inclusion of 1 mM-butyrate in glucose-containing medium had a similar inhibitory effect. Although cyclic nucleotide supported the acrosome reaction but not motility changes, no fertilization was obtained unless zonae were removed, when a low level of fertilization (30%) was observed. Both whiplash motility and acrosome loss are thus obligatory for sperm penetration of the zona and glycolytic metabolism supports both changes, perhaps by promoting endogenous generation of cyclic AMP to act as an intermediary in these two distinct phenomena.